Calibrating Device

ABSTRACT

A device ( 1 ) for calibrating geometrical measurements of surgical tools ( 10 ) as well as for orienting the same in space, including: A) a docking station ( 2 ) having two jaws ( 3 ) and a surface ( 21 ); and B) at least three marking indicators ( 9 ) firmly attached to the docking station ( 2 ) and capable of being measured, in reference to their position in space, electromagnetically or acoustically through a position detecting device ( 14 ), where C) the jaws ( 3 ) each have a lateral wall ( 40 ) so that the surface ( 21 ) and the lateral walls ( 21 ) of the two jaws ( 3 ) enclose a U-shaped passage ( 18 ), where D) the two jaws are conformed in a cylindrical or double conical manner; and E) the two lateral walls ( 40 ) or the surface ( 21 ) present a form comprising at least two additional contact points for a surgical tool ( 10 ) inserted between the jaws ( 3 ) across its longitudinal axis ( 11 ).

The invention refers to a device for calibrating geometric measurements,orienting and positioning of surgical tools in space, according to thegeneral concept of patent claim 1.

Such devices are suitable for the calibration of geometric measurements,especially of the diameter, position and/or orientation of surgicaltools in space. The calibration of the position and orientation is aboveall needed for surgical tools employed in computer-assisted surgery,where the position and orientation of various surgical tools ismeasured, during an operation, while using a surgical navigation systemincluding a position detecting device. Such a navigation system merelyallows determining the position of a marking indicator applied to thetool or a machine comprising the tool, for instance a drilling machine.An intra-operative calibration is for instance indispensable fordrilling processes where the drill, if inserted into a drilling machinein-situ, is inserted into a position with respect to the drillingmachine and the marking indicators which is previously unknown.

A device of this kind is known from the EP-A 0 904 735 MESSNER. Thisknown calibrating device also allows, apart from determining theposition of the tip of a tool, measuring the diameter of the tool byusing two jaws than can be shifted to each other in a linear manner.Before the measurement, the jaws must be shifted relative to each otherso as to precisely contact the mantle surface of the surgical tool alongtheir entire longitudinal axis parallel to the surgical tool. Thedisadvantage of this known device is that measuring errors may occur ifthe jaws cannot make proper contact over their entire length.

The invention intends to remedy this situation. The task underlying theinvention is to create a device capable of measuring essential geometricmeasurements, especially the diameter, width and height of longitudinal,prismatic or cylindrical objects having a centrally symmetrical crosssection, without requiring a shift of the jaws.

The invention solves the proposed task through a device for calibratinggeometric measurements and orienting surgical tools in space having thecharacteristics outlined in claim 1.

The advantages secured by the invention are essentially seen in the factthat tanks to the device according to the invention:

-   -   various cylindrical or prismatic surgical tools with a circular        or rectangular cross sectional surface can be docked to the        docking station in a position defined by the marking indicators;    -   cylindrical or prismatic surgical tools having other than        circular or rectangular cross sectional surfaces, for instance        oval or elliptical cross sectional surfaces, can be docked to        the docking station in a position defined by the operator;    -   the diameter of round cylindrical objects or the width or height        of objects with other cross sectional surfaces can be measured        without requiring a shift of the jaws;    -   the space orientation of various prismatic or cylindrical        surgical tools can be measured;    -   because the marking indicators, which are preferably applied on        a tool handle, meaning the tool shank at an axial distance,        generate a lengthening of the arms encompassing the angle α, so        that a small change of the angle α creates an additional        increase of the distances between the marking indicators on the        tool and those on the device, which makes it possible to achieve        a precision greater than that with shiftable jaws;    -   the jaws are locked to the docking station in an immovable        manner, so that while measuring no twisting or jamming can        occur.

Other favourable embodiments of the invention are characterized in thesubordinate claims.

In a preferred embodiment the jaws are, at least at their oppositesurface portions, conformed as double cones and comprise at their axialcentre an indentation penetrating across the central axis. The advantageof this conformation is essentially in the fact that the notched portionaids the jaws in positioning an inserted tool in a defined position. Theindentations of the jaws are preferably conformed in alignment with eachother, whereby the additional effect desirable for a measurement, thatof increasing the angle α at increasing diameter, is enhanced becauseboth contact points of the tool are diverging further from the centralaxes of the jaws.

The indentations are also preferably conformed in the shape of a V andhave a depth T across the central axis.

In a further embodiment the device additionally encompasses positioningmeans suitable for a precise positioning of the front ends of varioussurgical tools in relation to the docking station. This allows achievingthe advantages that the position of the front end, for instance of adrill bit, can be detected by the same device. Moreover, the position ofthe front end of a tool and its axis can be calibrated in series insuccessive independent steps. In the device divulged in EP-A 0 904 735MESSNER, a single working step must guarantee that the tool has beeninserted into the calibrating device up to the stop, and that both jawshave properly contacted the tool.

Again in another embodiment, the jaws are spaced from each other betweenat least 100 mm and 300 mm, so that the great distance of the jaws, whenmeasuring the angle, allow a high degree of precision when calibratingthe position of the longitudinal axis of the tool. The jaws are moreovernot movable with respect to the docking station.

In one more embodiment the device comprises a rotary table and a axis ofrotation extending across the surface, and two clamping jaws areprojecting above the surface, so that the surgical tool can bereleasable clamped on the rotary table of the device.

In another embodiment the docking station is fitted with a torsionspring, by which the rotary table is pushed in a first rotatingdirection around the axis of rotation. This allows the torsion spring topress a surgical tool, which has been obliquely inserted among the jaws,against the jaws in a self acting manner and without expending a manualforce, or to insert a surgical tool between the jaws in the case of aninversed rotation. It also guarantees that the tool is pressed againstboth jaws and rests on them in the desired defined position.

The rotary table is preferably movable, through an operating element,against the spring pressure in a second rotating direction around theaxis of rotation. This achieves the advantage that the rotary table can,through the operating element, be turned so as to allow inserting asurgical tool between the jaws, or in the case of an inverted rotation,to press it against the jaws. By assisting the one rotating direction byspring pressure and the other by hand pressure, a simple manual handlingof the device is assured.

The clamping jaws are preferably arranged on the rotary table so as tobe penetrated by a straight line crossing the axis of rotation, wherebyat a rotation of the rotary table in a first rotating direction theangle β enclosed between the straight line and the reference line isreduced, so that a surgical tool inserted between the jaws can bepressed against the jaws.

In a further embodiment a toothed-wheel gearing is installed between theoperating element and the rotary table.

The positioning means preferably include depressions having differentgeometric shapes and in particular different cross sectional surfaces.

In an additional embodiment the central axes of the jaws are setvertically to the surface. The jaws are also, at least on the surfaceportions opposing each other, conformed in a round cylindrical manner,while their surface is shaped in a flat manner. This allows attainingthe advantage that flat tools, for instance bits or saw blades can belaid down on the surface without causing a twist between the jaws.

The process of calibrating the geometric measurements of surgical toolsas well as their orientation in space essentially encompasses thefollowing steps:

A) inserting a surgical tool in a U-shaped passage formed by the surfaceof the docking station and by the two cylindrical or double cone-shapedjaws belonging to the docking station;

B) turning the surgical tool so as to reduce the angle α, which isenclosed by the longitudinal axis of the surgical tool and a referencestraight line defined by the shape of the jaws or the shape of the jawsand the surface, to the point that the mantle surface of the surgicaltool comes into contact with the lateral walls of the jaws in anorientation defined by the shape of the jaws, or by the shape of thejaws and the surface itself.

C) measuring, through a position detecting device, the spatialorientation of the marking indicators attached to a reference devicefastened to the docking station and to a reference device fastened tothe surgical tool,

D) determining the angle α from the measured positions of all themarking indicators by using a computer; and

E) determining the size of the surgical tool, which is verticallyextended between the central axes of the jaws, from the measured angle αand the known geometry of the jaws with respect to the markingindicators on the reference device of the docking station through acomputer.

In a preferred embodiment the process additionally includes thefollowing steps:

F) inserting the front end of a surgical tool in a depression providedon the docking station, where the position of the bottom of thedepression relative to the marking indicators on the reference device onthe docking station is already known; and

G) measuring the spatial position of the marking indicators, which areattached to the reference device fastened to the docking station and tothe reference device fastened to the surgical tool through a positiondetecting device;

H) determining the spatial position of the front end of the surgicaltool from the measured positions of all the indicators through acomputer.

The invention and the developments of the invention are in the followingexplained in further detail by using partially simplifiedrepresentations of several examples of embodiment.

These show:

FIG. 1 a perspective view of a form of embodiment of the deviceaccording to the invention, together with a surgical navigation system;

FIG. 2 a top view of a form of embodiment of the device according to theinvention;

FIG. 3 a longitudinal cross section through the form of embodiment ofthe device according to the invention shown in FIG. 2;

FIG. 4 a perspective view of the form of embodiment of the deviceaccording to the invention shown in the FIGS. 2 and 3.

FIG. 1 shows a form of embodiment of the device 1 which is essentiallyrealized by a docking station 2 fitted with two jaws 3 and a referencedevice 12 a, together with a drill held in a driving machine 15coaxially to its axis as a surgical tool 10, as well as by a positiondetecting device 14 and a computer 16. The jaws 3 and the surface 21encompass a U-shaped passage 18 (FIG. 3) suitable for passing alongitudinal surgical tool 10. The round cylindrical jaws 3 presentparallel central axes 24 which are set up centrally to the flat surface21 of the docking station 2. The surgical tool 10, meaning the drill, ispassed through the jaws 3 and rests, through its mantle surfaceconcentric to the longitudinal axis 11, at two points on the jaws 3 andthe surface 21, while the longitudinal axis 11 encloses an angle α withone of the reference straight lines 4 crossing the two central axes 24(FIG. 3) of the jaws 3 at right angles. An additional reference device12 b is provided on the driving machine 15. Both reference devices 12are fitted with four marking indicators 9 capable of being detectedelectromagnetically or acoustically, so that the spatial position of themarking indicators 9 can be measured through the position detectingdevice 14. Based on the measurement of the spatial position of themarking indicators 9, the computer 16 can then determine the position ofthe longitudinal axis 11 and of the reference straight line 4, as wellas the angle α enclosed between them. At a known value of the angle α,the known geometries of the two jaws 3 and of the surgical tool 10 allowdetermining the surgical tool 10, which is in this case conformed as adrill. In case of surgical tools 10 conformed in a different manner, themeasurement enclosed between the jaws 3 in a sense vertical to thecentral axes 24 is taken. The jaws 3 are firmly attached to the dockingstation 2 and in this case conformed in a round cylindrical fashion. Thedocking station 2 also includes a rotary table 6 with an axis ofrotation 25 extended vertically to the surface 21, which comprises twoclamping jaws 5 projecting above the surface 21. The rotary table 6 can,by using the handle 8 firmly attached to the docking station 2, berotated against the spring pressure of a torsion spring 26 (FIG. 3)around the axis of rotation 25. If the operating lever 17 is not underthe action of a force, the rotary table 25 is moved by the force of thetorsion spring 26 (FIG. 3) in a first direction of rotation 27, so thatthe surgical tool 10 passed between the jaws 3 is pressed, by theclamping jaws 5 arranged on the rotary table 6, against the jaws 3. Ifthe operating lever 17 is pressed against the handle 8, the rotary table6 is moved in the opposite second direction 28, so that a surgical tool10 can, without being hampered by the clamping jaws 5, be inserted intothe docking station 2. The rotary table 6 is in this case conformed in acircular shape concentric to the axis of rotation 25, while the twoclamping jaws 5 are arranged in a diagonal direction.

The FIGS. 2 and 3 represent a form of embodiment of the device 1, whosesquare shaped docking station 2 comprises two jaws 3 set up on thesurface 21 in a diagonal direction. The jaws 3 are conformed on thesurface portions opposite to each other in a double-conical form, andare thus fitted, at an axially central point, with a V-shapedindentation 13 penetrating into the jaws 3 across the central axes 24,so as to achieve a defined position of a surgical tool 10 against thejaws 3. The central axes 24 are defined by the centres of two conical,circular sector-shaped cross sectional surfaces per jaw 3. Theindentations 13 on the lateral walls 40 have, if measured across thecentral axes 24, a depth T and are aligned with each other. The surgicaltool 10 is inserted between the jaws 3 so that its longitudinal axis 11passes between the jaws 3 and that the mantle surface of the surgicaltool 10, which is concentric to the longitudinal axis 11, rests at twopoints, respectively, inside each of the two indentations 13 on the twolateral walls 40 of the jaws 3. Moreover, a toothed wheel-gearing 29 isdisposed between the axis 33 of the rotary table 6 and the front end 34of the operating lever 17. The docking station 2 pictured here exhibitsfour lateral surfaces 41;42;43;44, where the reference devices 12 areapplied to the first lateral surfaces 41 through four marking indicators9 capable of being detected electromagnetically or acoustically. Thehandle 8, along with the operating lever 17, is arranged on theopposite, second lateral surface 42. The operating lever 17 is passedthrough an opening 35 into the central hollow space 36 which is openagainst the bottom surface 18 of the docking station 2, and is fastenedwith its front end 34 to the axis 38 of the first toothed gear 37, whichis connected to the docking station 2 in a rotating manner. The firsttoothed gear 37 is engaged with a second toothed gear 39, which islikewise fastened to the axis 33 of the rotary table 6 which isconnected to the docking station 2 in a rotating manner. The axis 33 ofthe rotary table 6 runs coaxially to the axis of rotation 25 of therotary table 6 and is set vertically to the surface 21. Two clampingjaws projecting beyond the surface 21 are also arranged on the rotarytable 6. The rotary table 6 is conformed on its cross sectional surfaceset orthogonally to the axis of rotation 25 in a circular manner, whilethe two clamping jaws 5 are arranged in a diagonal direction. A torsionspring 26 concentric to the axis of rotation 25, which presses therotary table 6 in a first rotating direction 27, is also arrangedbetween the docking station 2 and the second toothed gear 39. By usingthe operating lever 8, the rotary table 6 can be moved in the seconddirection of rotation against the force of the spring. The force of thetorsion spring 26 allows achieving the action of moving the rotary table6 in the first direction of rotation 27, so that the angle β enclosedbetween the straight line 7 crossing then axis of rotation 25 andcentrally penetrating the clamping jaws and the reference straight line4 (FIG. 1) is reduced, and that a surgical tool 10 inserted between thejaws 3 is pressed against the jaws 3.

FIG. 4 shows a form of embodiment comprising positioning means 30arranged on a third lateral surface 43 of the docking station 2, so asto position the front ends 31 (FIG. 2) of various surgical tools 10 withrespect to the docking station 2. These positioning means 30 comprisedepressions 32 having geometries differing from each other for a definedreception of different surgical tools 10 (FIGS. 1;2). In particular, thedepressions 32 a;32 b;32 c;32 d are conformed so that:

-   -   The depression 32 a presents a rectangular entrance opening        parallel to the third lateral surface 43 and tapering from the        long sides of the entrance opening toward the bottom of the        depression 32 a, so as to make it suitable for receiving the        front ends of for instance a flat chisel;    -   The depression 32 b is conformed as a slot with a flat bottom of        the depression 32 b, so as to be suitable for receiving the        front end of for instance a saw blade;    -   The depression 32 c is conformed in a conical shape and suitable        for centering the tip of for instance a pointer; and    -   The depression 32 d is conformed as a round cylindrical borehole        with a flat bottom, so as to be suitable for receiving        cylindrical tools with various tips.

1. A device (1) for calibrating geometrical measurements of surgicaltools (10) and orienting the same in space, comprising: A) a dockingstation (2) having two jaws (3) and a surface (21); and B) at leastthree marking indicators (9) arranged on the docking station (2) in afixed manner and measurable in reference to their spatial positionelectromagnetically or acoustically, in order to determine the positionand orientation of the device (1) in space through a position detectingdevice (14), C) wherein the jaws (3) are stationary with respect to thesurface (21) of the docking station (2) and have one lateral wall (40)each, so that the surface (21) and the lateral walls (40) of the twojaws (3) encompass a U-shaped passage (18); D) wherein the two jaws (3)are, at least on the surface portions opposite to each other, conformedin a round cylindrical, hyperboloid or double-cone shaped fashion, sothat a surgical tool (10) which has been inserted between the jaws (3)can be laid down on at least one contact point of each jaw (3) acrossits longitudinal axis (11), E) wherein the device (1) further comprisesa rotary table (6) with an axis of rotation (25) running across thesurface (21) and two clamping jaws (5) projecting over the surface (21);and F) the two lateral walls (40) or the surface (21) or the rotarytable (6) have a form comprising at least two additional points ofcontact for a surgical tool (10) inserted between the jaws (3) acrossits longitudinal axis (11), so as allow a lateral docking, defined withrespect to the marking indicators (9), of a surgical tool (10) passedbetween the jaws (3).
 2. The device (1) according to claim 1, whereinthe two jaws (3) are, at least on their surface portions opposite toeach other, conformed in a double-conical form comprising, in an axiallycentral point a V-shaped indentation (13) and having a central axis (24)defined by the centers of the circular or circle sector-shaped conecross sectional surfaces.
 3. The device (1) according to claim 1,wherein the indentations (13) of the two jaws (3) have a depth T and areconformed in a manner aligned to each other.
 4. The device (1) accordingto claim 3, wherein the angle α between one of the reference straightlines (4) that penetrate the lateral walls (40) in the indentations (13)at the depth T and cross the central axes (24) and the longitudinal axis(11) of a docked surgical tool (10) is α<90°.
 5. The device (1)according to claim 1, wherein the device additionally comprisespositioning means (30) to position the front ends (31) of differentsurgical tools (10) with respect to the docking station (2).
 6. Thedevice (1) according to claim 1, wherein the jaws (3) have a distancefrom each other of at least between 100 mm and 300 mm.
 7. The device (1)according to claim 1, wherein the jaws (3) have central axes (24) thatare parallel to each other.
 8. The device (1) according to claim 1,wherein a torsion spring (26) is arranged on the docking station (2),whereby the rotary table (6) is pressed in a first rotating direction(27) around the axis of rotation (25).
 9. The device (1) according toclaim 8, wherein the rotary table (6) can be moved through an operatingelement (8) against the force of the spring in a second direction ofrotation around the axis of rotation (25).
 10. The device (1) accordingto claim 4, wherein the clamping jaws (5) are arranged on the rotarytable (6) so as to be centrally penetrated by a straight line (7)crossing the axis of rotation (25).
 11. The device (1) according toclaim 10, wherein at a rotation of the rotary table (6) in a firstdirection of rotation (27), the angle β enclosed between the straightline (7) and the reference straight line (4) is reduced, so that asurgical tool (10) inserted between the jaws (3) can be pressed againstthe jaws (3).
 12. The device (1) according to claim 9 wherein atoothed-wheel gearing (29) is arranged between the operating element (8)and the rotary table (6).
 13. The device (1) according to claim 5wherein the positioning means (32) comprise depressions (30) havinggeometries differing from each other.
 14. The device (1) according toclaim 13, wherein the depressions (32) have different cross sectionalsurfaces.
 15. The device (1) according to claim 1, wherein the jaws (3)cannot be moved with respect to the docking station (2).
 16. The device(1) according to claim 1, wherein the surface (21) is conformed in aflat manner and that the jaws (3) are of a round cylindrical form atleast in the surface portions opposite to each other.
 17. A process forcalibrating geometrical measurements of surgical tools (10) as well asfor orienting the same in space, comprising the following steps: A)inserting a surgical tool (10) into a U-shaped passage (18), formed bythe surface (21) of a docking station (2) and two round cylindrical ordouble cone-shaped jaws (3) belonging to the docking station (2); B)rotating the surgical tool (10) so that the angle α, which is enclosedby the longitudinal axis (11) of the surgical tool (10) and by areference straight line (4) defined by the shape of the jaws (3) or theshape of the jaws (3) and the surface (21), is reduced to the point thatthe mantle surface of the surgical tool (10) comes to rest against thelateral walls (40) of the jaws (3) at an orientation defined by the formof the jaws (3), or the form of the jaws (3) and the surface (21); C)pressing the surgical tool (10) against the jaws (3) by means of theclamping jaws (5) arranged on the rotary table (6); D) measuring thespatial position of the marking indicators (9) fastened to the dockingstation (2) and to the surgical tool (10), through a position detectingdevice (14); E) determining the angle α from the measured positions ofall marking indicators (9) through a computer (9); and F) determiningthe diameter extending vertically to the central axes (24) of the jaws(3) or the width of the surgical tool (10) from the measured angle α andthe known geometry of the jaws (3) with respect to the markingindicators (9) on the docking station (2) through a computer (16). 18.The process according to claim 17, additionally comprising the followingsteps: F) inserting the front end (31) of a surgical tool (10) into oneof the depressions (32) provided on the docking station (2), where theposition of the bottom of the depression (32) with respect to themarking indicators (9) on the reference device (12 a) of the dockingstation (2) is known; G) measuring the spatial position of the markingindicators (9) that are fastened to the docking stations (2) and to thesurgical tool (10) through a position detecting device (14); and H)determining the spatial position of the front end (31) of the surgicaltool (10) from the measured positions of all the marking indicators (9)through a computer (16).